SlackBuildsOrg/office/osmo-gtk2

This is the last GTK2 version of Osmo. It will conflict with the latest
one, so don't install both.

Osmo is a handy personal organizer, which includes calendar, tasks
manager, contacts and notes modules. It was designed to be a small,
easy to use and good looking PIM tool to help to manage personal
information. In its current state the  organizer is quite convenient
to use - for example, the user can perform nearly all operations using
the keyboard. Also, a lot of parameters are configurable to meet the
user's preferences. On the technical side, Osmo is GTK+3 based tool
which uses a plain XML database to store all personal data.